### Use the `app.dependency_overrides` attribute { #use-the-app-dependency-overrides-attribute }

For these cases, your **FastAPI** application has an attribute `app.dependency_overrides`, it is a simple `dict`.

To override a dependency for testing, you put as a key the original dependency (a function), and as the value, your dependency override (another function).

Hiding the documentation just makes it more difficult to understand how to interact with your API, and could make it more difficult for you to debug it in production. It could be considered simply a form of <a href="https://en.wikipedia.org/wiki/Security_through_obscurity" class="external-link" target="_blank">Security through obscurity</a>.

If you want to secure your API, there are several better things you can do, for example:

# limitations under the License.
# ==============================================================================
if [[ "$TFCI_DOCKER_PULL_ENABLE" == 1 ]]; then
  # Simple retry logic for docker-pull errors. Sleeps if a pull fails.
  # Pulling an already-pulled container image will finish instantly, so
  # repeating the command costs nothing.
  docker pull "$TFCI_DOCKER_IMAGE" || sleep 15

    "JDK17",

    "JDK_HOME",
    "JRE_HOME",
    "CommonProgramFiles",
    "CommonProgramFiles(x86)",
    "CommonProgramW6432",
    "ProgramData",
    "ProgramFiles",
    "ProgramFiles(x86)",
    // Simply putting PATH there isn't enough. Windows has case-insensitive env vars but something else fails if the Path variable is published as PATH for test tasks.
    OperatingSystem.current().pathVar,
    "PATHEXT",

     * If this method returns <code>null</code> the <code>SmbAuthException</code> that triggered the authenticator check will simply be rethrown. The default implementation returns <code>null</code>.
     * @return the authentication credentials or null if none available
     */
    protected NtlmPasswordAuthentication getNtlmPasswordAuthentication() {

Así que, puedes usar `user_agent` como normalmente lo harías en código Python, en lugar de necesitar capitalizar las primeras letras como `User_Agent` o algo similar.

Si por alguna razón necesitas desactivar la conversión automática de guiones bajos a guiones, establece el parámetro `convert_underscores` de `Header` a `False`:

    builder.setSafeRange(' ', '~');
    assertThat(builder.build().escape("The Quick Brown Fox!")).isEqualTo("The_Quick_Brown_Fox_");
  }

  public void testBuilderCreatesIndependentEscapers() {
    // Set up a simple builder and create the first escaper.
    Escapers.Builder builder = Escapers.builder();
    builder.setSafeRange('a', 'z');
    builder.setUnsafeReplacement("X");
    builder.addEscape(' ', "_");

@GwtCompatible
abstract class CollectionFuture<V extends @Nullable Object, C extends @Nullable Object>
    extends AggregateFuture<V, C> {
  /*
   * We access this field racily but safely. For discussion of a similar situation, see the comments
   * on the fields of TimeoutFuture. This field is slightly different from the fields discussed
   * there: cancel() never reads this field, only writes to it. That makes the race here completely

          submittingTaskQueue.nextTask = task;
          // requireNonNull(delegate) is safe for reasons similar to requireNonNull(sequencer).
          submittingTaskQueue.nextExecutor = requireNonNull(delegate);
          delegate = null;
        } else {
          // requireNonNull(delegate) is safe for reasons similar to requireNonNull(sequencer).
          Executor localDelegate = requireNonNull(delegate);
          delegate = null;

We see that we are going to need some dependencies used in several places of the application.

So we put them in their own `dependencies` module (`app/dependencies.py`).

We will now use a simple dependency to read a custom `X-Token` header:

{* ../../docs_src/bigger_applications/app_an_py39/dependencies.py hl[3,6:8] title["app/dependencies.py"] *}

/// tip